1. Field of the Invention
The invention relates in general to a D-class audio power amplifier and method thereof, and more particularly to a D-class audio power amplifier driven by a micro-processor and method thereof.
2. Description of the Related Art
Compared with an A-class or a linear power amplifier, a D-class audio power amplifier has the features of low heat-radiation and low power-consumption and is often used in an LCD TV to power-amplify the input audio signal.
Referring to FIG. 1A, a circuit block diagram of a conventional D-class audio power amplifier is shown. A D-class audio power amplifier 100 includes a pulse-wave generator 110, a modulator 120, a power amplifier 130 and a low-pass filter 140. The pulse-wave generator 110 is used to generate a triangle wave WT. The modulator 120 is used to mix an input audio signal Sa with the triangle wave WT to be compared with a reference voltage Vf then outputs a pulse width modulation (PWM) signal SP. The power amplifier 130 power-amplifies the PWM signal to obtain a power-amplified signal, then the low-pass filter 140 filters the high-frequency signal portion off the power-amplified signal to output an amplified audio signal So. Moreover, the power amplifier 130, which is normally operated under single power and has a single input voltage Vcc, generates a higher operating voltage (VDD) via a charge pump (not shown in the diagram) to control the transistor switching operation of the control power amplifier 130.
Besides, the current requirement of the power consumption for the LCD TV under power-saving mode is almost under 1 Watt. Therefore, the display control circuit of the LCD TV normally adopts a Central Processor Unit (CPU), whose function is simple and power-consumption is low such as an integrated circuit with an 8051 processor, as a control circuit to awake the pixel-works when the LCD TV is under power-saving mode.
Referring to FIG. 1B, a circuit structural diagram of a power-saving system of an LCD TV according to prior arts is shown. The 8051 processor 150 is at idle state when the LCD TV is under normal operation. When the LCD TV is operating under power-saving mode, only the processor 150 is at operating state, while other parts such as a pixel-works 160 are all at power-off state. Meanwhile, the 8051 processor 150 can be controlled by an external signal S such as a remote control signal to switch on a switch 170 for the power of a power module 180 to be inputted into the pixel-works 160 to awake the entire system. The low power-consumption CPU is at idle state when the system is under normal system operation. The system manufacturing costs can be reduced if the CPU is wisely used to drive a D-class amplifier.